Ultrasound imaging can be a useful tool in cardiology, such as, for example, in the diagnosis of myocardial infarctions. Ultrasound imaging of the heart, known as echocardiography, can be used, for example, to derive strains, which are related to the contractility of the heart muscle. However, current methods of real-time raw data acquisition of a full view of the heart limit the data acquisition rate to 50 frames per second (fps). It is noted that a “full view” is actually the default size of an image plane in a given system, which can be defined by a spanned angle (i.e., arc length according to the center of an imaging probe) and a chosen depth (beam direction). Tracking rapid motion of the heart in a short period or depicting the high-speed electro-mechanical wave propagating in the heart at frame rates of 50 fps is difficult. Moreover, because strains involve motion of the heart muscle, a frame rate (effectively a sampling rate of the displacement function over time) is required to be high enough such that interframe motion is relatively small to be accurately estimated. Using conventional frame rates, strain image results tend to be both noisy and unreliable This is because the lower the frame rate, the less correlated any two consecutive frames are, which makes radio-frequency (RF)-cross-correlation based motion estimation techniques less accurate. One quantitative measure of the noise on strain images is the elastographic signal-to-noise ratio, or SNRe.
With the high frame-rate composite imaging, precise and detailed motion/strain estimates in full view can be obtained and further used to differentiate abnormal from the normal myocardium and even detect the onset and extent of the diseased muscle. From theoretical and in vivo examples, the difference between strain in a normal and an abnormal myocardium can be large in the case of acute infarction but also subtle in the case of chronic infarction, infarction scars or small infarcted regions. Visualization in the latter case is more challenging and an imaging modality that estimates the strain at high precision and thus SNRe is warranted. RF-based tracking can provide such precision to estimate subtle motion changes in the pathological myocardium. Most importantly, the ischemic region will undergo abnormal, i.e., smaller or reverse, motion due to its reduced contractility. Estimation of the resulting smaller motion and/or strain (compared to the normal case) also requires higher precision of the method used. Again, RF-based tracking (as opposed to the faster and more commonly used B-mode tracking) will yield the highest precision estimate and thus highest quality images. Due to the higher sensitivity of RF-based tracking, i.e., the higher decorrelation rate, RF tracking is best used at the highest frame rates, where consecutively acquired RF echoes are best matched because they are recorded at small incremental time intervals.
In a similar way, the same invention can be applied for visualization of all transient motion effects in tissues or vessels, such as the pulse wave traveling in the arterial tree at each heartbeat, respiratory motion, or the pulsation of internal vessels in organs, such as the liver, pancreas, kidney, thyroid or prostate.
What is thus needed in the art are systems and methods that can increase the ultrasound frame rate so as to be sufficiently high to capture cardiac motion and provide meaningful strain image results.